OBJECTIVES AND AIMS: Although brain extracellular matrix and fluid control neuronal function relatively little is known about them. Molecular movement in the extracellular space depends on hydrostatic and osmotic pressure gradients, the chemical composition of the matrix, and the pathways between cells. In order to study transport in the extracellular fluid, we developed 14C-sucrose autoradiography to measure apparent diffusion coefficients in periventricular tissue exposed to the isotope during ventriculocisternal perfusion in the cat. The autoradiographic method is comparable to the standard tissue sectioning methods used to obtain diffusion constants. We propose to use the method to examine the effect of mannitol-induced serum hyperosmolality and enzyme hyaluronidase on extracellular molecular movement. Mannitol lowers intracranial pressure and appears to enhance extracellular fluid movement. Hyaluronidase acts on hyaluronic acid to enhance extracellular movement in ischemic myocardium. Recently hyaluronidase was shown to be of benefit in the gerbil stroke model. Analysis of extracellular transport and testing of agents that may enhance interstitial fluid flow is important in understanding the pathophysiology of cerebral edema and stroke and in the planning of possible therapeutic trials in these conditions. METHODS: Experiments are planned in anesthetized adult cats. Ventriculocisternal perfusion or intracerebral injection will be done with 14C-sucrose (m.w. 341) or 14C-polyethylene glycol (m.w. 4000). After perfusion or injection brains are removed and prepared for autoradiography. Isotope concentrations in tissues will be measured from the autoradiograms by computer-assisted image processing. Apparent diffusion coefficients and rates of bulk flow of interstitial fluid are calculated in one-dimension. At a later time analysis of diffusion in two-dimensions is planned. Further experiments are planned to test the effect of the enzyme, hyaluronidase, and of the osmotic agent, mannitol, on molecular movement in the extracellular space.